This project deals with sequential CT evaluation of elderly subjects who have well-defined mild senile dementia of the Alzheimer type (SDAT) and matched healthy controls in a longitudinal investigation. These CT studies are, in turn, to be correlated with the clinical assessment, psychometric evaluation, EEG, evoked potentials, etc. PET studies are also planned at designated intervals on these subjects. "Cross-sectional" assessments will be done and will be compared with the results of the longitudinal study. The proposal calls for quantitative CT evaluation consisting of measurement of volume of brain and cerebro-spinal fluid (CSF) spaces and cranial volume. These CT measurements will be correlated with clinical examinations, behavioral and other studies to determine whether the CT findings can help differentiate changes associated with healthy aging from those associated with SDAT. Based on these correlative studies the goal of the project is to determine the value of CT findings in predicting the clinical course of the subjects or changes in behavioral and physiological measures.